<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .aqua{
            background-color: aqua;
        }
        .red{
            background-color: red;
        }
    </style>
</head>
<body>
    <button class="aqua">按钮1</button>
    <button class="red">按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
<script>
    let bts = document.querySelectorAll('button')
    for (let i = 0; i < bts.length; i++) {
        bts[i].addEventListener('click', function () {
            document.querySelector('.pink').className = ''
            this.className = 'pink'
         })
    }
</script>
</body>
</html>